1. Field of the Invention
The present invention relates to a method for forming pin-form wires or bumps.
2. Prior Art
Pin-form wires and bumps are generally distinguished according to the presence or absence of wire or to the length of wire remaining on the ball bonded to the electrode pad of an electronic circuit element, etc. However, this distinction is not very strict. In the following description, cases in which the length of the wire described above is long, e.g., 100 to 500 xcexcm, will generally be referred to as pin-form wires, while cases in which the length of the above-described wire is shorter than this will be referred to bumps.
Conventional method for forming pin-form wires or bumps is disclosed in, for example, the Japanese Patent Application Laid-Open (Kokai) H10-135220. The title of this prior art is xe2x80x9cA Bump Forming Method.xe2x80x9d However, this prior art shows a wire that has a certain length and is formed on the ball which is bonded to the electrode pad of an electronic circuit element, etc. Accordingly, this method can be viewed as a method for forming a pin-form wire.
In this prior art, a ball is formed on the tip end of a wire that passes through a capillary, and this ball is bonded to the electrode pad of an electronic circuit element, etc., using the capillary. Then, the capillary is raised for a predetermined amount, and the wire is cut at the lower end of the capillary at a position that is sufficiently away from the ball, so that a pin-form wire or bump is formed. Cutting of the wire in this prior art is performed by one of the methods described below:
In the first method, an electric discharge is applied to the wire, that is located at the capillary hole tip, by means of a discharge electrode installed on the side of the capillary.
In the second method, laser beam is irradiated to the wire, that is at the capillary hole tip end, by means of a laser installed on one side of the lower end of the capillary.
In the third method, air is blown to the wire, that is at the capillary hole tip end, by means of an air nozzle installed on one side of the tip end of the capillary.
In the fourth method, a capillary that is formed by a plurality of chucking pieces which are capable of clamping down on the wire and then releasing the wire, or a capillary that has a chucking means only at its tip end portion, is used; and notches are formed on the wire, that is at the capillary hole tip end, by the edge of the capillary, and then a tensile force is applied to the wire so as to cut the wire.
In the fifth method, a cutter is positioned on one side of the capillary, and the cutter is pressed against the wire, that is at the capillary hole tip end, thus cutting the wire.
In the sixth method, strained portions are formed by notches, press grooves, etc. beforehand at equal intervals along the direction of the length of the wire that is passed through the capillary, and the wire is cut by applying a tensile force to the wire.
In the above-described first method, the cutting of the wire is accomplished by causing an electrical discharge on the wire that is at the capillary hole tip end. Accordingly, the wire is melted by the discharge, and the molten wire rises into the capillary hole, resulting in that the capillary hole is clogged.
In the above-described second, third and fifth methods, it is difficult to install a laser device, an air nozzle and a cutter in the area that has extremely short wire length of, for example, 500 xcexcm or less, between the ball that is bonded to the electrode pad and the capillary that is in a raised position. Accordingly, such methods are not realized unless there is a certain length of wire present between the ball and the capillary. Furthermore, in cases where numerous pin-form wires or bumps are formed in a dense concentration on an electronic circuit element, etc., the cutting means such as a laser device, air nozzle or cutter contacts the pin-form wires or bumps. Thus, such cutting means cannot be installed.
In the above-described fourth method, the capillary is formed as chucking pieces or has a chucking part that can be freely opened and closed. In this method,.however, since in the case of in ultrasonic bonding the structure of the capillary affects the bondability, it is difficult to form a capillary of a chucking structure. Thus, the fourth method that uses capillaries is impractical.
In the above-described sixth method, it is necessary to form strained portions at equal intervals in the wire beforehand in the wire manufacturing process. Accordingly, there are an increased number of processes required for wire manufacture, and material costs are increased. Furthermore, the diameter of the wire is generally extremely small and as slender as, for instance, 20 to 50 xcexcm, and since back tension is applied to the portion of the wire located between the capillary and the spool on which the wire is wound, there is a danger that arbitrary strained portions of wire between the spool and the capillary might be twisted by this back tension, and the wire is cut as a result of this strain and other reasons. Moreover, the length of the wire allowed above the bonded ball is limited.
Accordingly, the object of the present invention is to provide a method for forming pin-form wires and the like (bumps) which makes it possible to set the length of the wire above the ball bonded to an electronic circuit element, etc. for any desired length and which involves no cost increase.
The above object is accomplished by a unique process of the present invention used in a method for forming pin-form wires and the like, in which: a ball is formed on the tip end of a wire passed through a capillary of a wire bonding apparatus, the ball is bonded to the electrode pad of an electronic circuit element, etc., using the capillary, the capillary is raised by a fixed amount, and a pin-form wire, etc. is formed by cutting the portion of the wire located above the ball; and in the present invention, the length of the wire extending from the lower end of the capillary is set longer than the wire length required for forming the ball that is formed in the next step, a ball is formed on the tip end of the wire, notches are formed in the portion of the wire located between the ball and the capillary by means of cutters provided in the wire bonding apparatus, the ball is bonded to the electrode pad, and the wire is pulled upward so that the wire is cut from the area of the notches.
The above object is accomplished by another unique process of the present invention used in a method for forming pin-form wires and the like, in which a ball is formed on the tip end of a wire passed through a capillary of a wire bonding apparatus, the ball is bonded to the electrode pad of an electronic circuit element, etc., using the capillary, the capillary is raised by a fixed amount, and a pin-form wire, etc. is formed by cutting the portion of the wire located above the ball; and in the present invention, the length of the wire extending from the lower end of the capillary is set longer than the wire length required for forming the ball that is formed in a later step, notches are formed in the portion of the wire located between the ball and the capillary by means of cutters provided in the wire bonding apparatus, a ball is formed on the tip end of the wire, the ball is bonded to the electrode pad, and the wire is pulled upward so that the wire is cut from the area of the notches.